The linear induction motor (LIM) and linear synchronous motor (LSM) are the two conventional linear (motion in a straight line, rather than circular) electric motors. The segmented rail phased induction motor (SERAPHIM) is a recently developed linear electric motor which, although inductive, is very different from a LIM.
A LIM for vehicle applications has an elongated, fixed, reaction rail adjacent the path of the vehicle, and a stator coil carried by the vehicle in reactive proximity to the reaction rail. Operation of the LIM results from the stator embedding magnetic flux in the conducting reaction rail and then interacting with this transient embedded flux. The LIM has two important limitations. First, the time required to embed flux limits the speed at which a LIM can operate, necessitating longer coils for higher speed. Second, the embedded magnetic flux left behind represents an energy loss which hurts the efficiency.
A typical LSM consists of a moving electromagnet and a sequence of coils which are energized in phase with the moving magnet to either attract or repel it. This motor can be quite efficient, especially if the moving electromagnet coil is superconducting. It does, however, efficient, especially if the moving electromagnet coil is superconducting. It does, however, require the entire length of the excursion to be switched and powered, which is costly and restricts its use to places where ample power is available.
SERAPHIM, as disclosed in U.S. Pat. No. 5,552,649 of Cowan and Marder, the disclosure of which patent is incorporated herein by reference thereto, resembles a LSM in that a moving coil interacts with a series of secondary conductors consisting of solid conducting plates, possibly configured in axe2x80x9csegmented railxe2x80x9d. Unlike a LIM, this motor uses high frequency pulses (KHz) in the powered coil to induce surface currents in the plates. The pulses are delivered when the plates are in position to produce a force in the desired direction. By operating at high frequency, the current remains near the surface so little flux penetrates the plates. Thus, whereas a conventional LIM operates by embedding flux in a continuous conductor, SERAPHIM operates by excluding flux from the interior and using the edge surface currents to produce the force. Since there is no time required for flux penetration, this motor is capable of much higher speed with no minimum length requirement.
Since the Seraphim motor relies on the exclusion of flux from the reaction rail, it has the following advantages over conventional LIMs for use as a high-speed rail propulsion technology:
It permits a larger gap between the active coil and the reaction rail, at least 2.5 cm (1xe2x80x3), which improves ride quality and relaxes guideway tolerances, significantly reducing construction and maintenance costs.
Very low magnetic drag is induced in the reaction rail (assuming proper motor control), which improves motor efficiency.
It is smaller, lighter, and more compact than a conventional LIM, and has been estimated to cost significantly less to build and operate.
The efficiency of the motor increases with speed.
High frequency operation of the SERAPHIM does have a drawback. The powered SERAPHIM coils have a high inductance, so the circulating power in the coils increases with frequency for a fixed mechanical power. This factor increases the size, weight, and cost of the motor. Furthermore, since electrical power handling equipment is more readily available at standard power frequencies (50 and 60 Hz), there are advantages to operating at these low frequencies. While the solid plates of the SERAPHIM rail could be used at these frequencies, improved performance is realized by replacing the plates with a circuit. The Dual-Circuit SERAPHIM (DCS) is a variation of SERAPHIM which is more efficient and has better electrical properties. The envisioned use of this motor is vehicle propulsion.
It is an object of this invention to provide a SERAPHIM that can operate efficiently at low frequency.
To achieve the foregoing object, and in accordance with the purpose of the present invention, as embodied and broadly described herein, the present invention may comprise an efficient dual circuit linear motor comprising a powered first circuit comprising a flat powered coil of an elongated electrical conductor having a first end at an inside of the coil and a second end at an outside of the coil; and a source of low frequency AC power connected across the conductor ends. This coil faces a segmented reaction rail comprising a plurality of aligned track circuits, each track circuit comprising a flat track coil of elongated electrical conductor having a first end at an inside of the track coil and a second end at an outside of the track coil, the first end being electrically shorted to said second end by a short length of conductor. The powered coil is in a first plane and the track coils are in a second plane parallel to the first plane, and the powered coil is aligned with and spaced from said track coils so the powered coil can move along said reaction rail.
Additional objects, advantages, and novel features of the invention will become apparent to those skilled in the art upon examination of the following description or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained as particularly pointed out in the appended claims.